Liquid-crystalline medium and liquid-crystal display

ABSTRACT

The present invention relates to dielectrically positive liquid-crystalline media comprising in each case one or more compounds of the formula I 
                         
in which the parameters have the respective meanings indicated in the specification, and optionally one or more further dielectrically positive compounds and optionally one or more further dielectrically neutral compounds, and to liquid-crystal displays containing these media, especially to active-matrix displays and in particular to TN, IPS and FFS displays.

FIELD OF THE INVENTION

The present invention relates to liquid-crystalline media and toliquid-crystal displays containing these media, especially to displaysaddressed by an active matrix and in particular to displays of thetwisted nematic (TN), in-plane switching (IPS) or fringe-field switching(FFS) type.

STATE OF THE ART AND PROBLEM TO BE SOLVED

Liquid-crystal displays (LCDs) are used in many areas for the display ofinformation. LCDs are used both for direct-view displays and forprojection-type displays. The electro-optical modes used are, forexample, the twisted nematic (TN), super twisted nematic (STN),optically compensated bend (OCB) and electrically controlledbirefringence (ECB) modes together with their various modifications, aswell as others. All these modes utilise an electric field which issubstantially perpendicular to the substrates or the liquid-crystallayer. Besides these modes, there are also electro-optical modes thatutilise an electric field which is substantially parallel to thesubstrates or the liquid-crystal layer, such as, for example, thein-plane switching (IPS) mode (as disclosed, for example, in DE 40 00451 and EP 0 588 568) and the fringe field switching (FFS) mode, inwhich a strong “fringe field” is present, i.e. a strong electric fieldclose to the edge of the electrodes and, throughout the cell, anelectric field which has both a strong vertical component and a stronghorizontal component. These latter two electro-optical modes inparticular are used for LCDs in modern desk-top monitors and areintended for use in displays for TV sets and multi-media applications.The liquid crystals according to the present invention are preferablyused in displays of this type. In general, dielectrically positiveliquid-crystalline media having rather lower values of the dielectricanisotropy are used in FFS displays, but in some casesliquid-crystalline media having a dielectric anisotropy of only about 3or even less are also used in IPS displays.

For these displays, novel liquid-crystalline media having improvedproperties are required. The addressing times in particular have to beimproved for many types of application. Thus, liquid-crystalline mediahaving lower viscosities (η), especially having lower rotationalviscosities (γ₁), are required. In particular for monitor applications,the rotational viscosity should be 80 mPa·s or less, preferably 60 mPa·sor less and especially 55 mPa·s or less. Besides this parameter, themedia must have a nematic phase range of suitable width and position andan appropriate birefringence (Δn), and the dielectric anisotropy (Δ∈)should be sufficiently high to allow a leasonably low operating voltage.Δ∈ should preferably be greater than 2 and very preferably greater than3, but preferably not greater than 15 and in particular not greater than12, as this would prevent an at least fairly high resistivity.

For applications as displays for notebooks or other mobile applications,the rotational viscosity should preferably be 120 mPa·s or less andparticularly preferably 100 mPa·s or less. The dielectric anisotropy(Δ∈) here should preferably be greater than 8 and particularlypreferably greater than 12.

The displays according to the present invention are preferably addressedby an active matrix (active matrix LCDs, AMDs for short), preferably bya matrix of thin film transistors (TFTs). However, the liquid crystalsaccording to the invention can also advantageously be used in displayshaving other known addressing means.

There are numerous different display modes which use composite systemsof low-molecular-weight liquid-crystal materials together with polymericmaterials. These are, for example, polymer dispersed liquid crystal(PDLC), nematic curvilinearly aligned phase (NCAP) and polymer network(PN) systems, as disclosed, for example, in WO 91/05 029, or axiallysymmetric microdomain (ASM) systems and others. In contrast to these,the modes that are especially preferred in accordance with the presentinvention use the liquid-crystal medium as such, oriented on surfaces.These surfaces are typically pretreated in order to achieve uniformalignment of the liquid-crystal material. The display modes according tothe present invention preferably use an electric field which issubstantially parallel to the composite layer.

Compounds of the formula

in which R denotes H, alkyl or alkenyl, are, besides others, mentionedin DE 10 2007 038 618 A1.

Liquid-crystal compositions which are suitable for LCDs and especiallyfor IPS displays are known, for example, from JP 07-181 439 (A), EP 0667 555, EP 0 673 986, DE 195 09 410, DE 195 28 106, DE 195 28 107, WO96/23 851 and WO 96/28 521. However, these compositions have severedisadvantages. Amongst other deficiencies, most of them result indisadvantageously long addressing times, have inadequate values of theresistivity and/or require excessively high operating voltages. Inaddition, there is a demand for improving the low-temperature behaviourof LCDs. Both an improvement in the operating properties and also in theshelf life are necessary here.

Thus, there is a considerable need for liquid-crystalline media havingsuitable properties for practical applications, such as a broad nematicphase range, suitable optical anisotropy Δn corresponding to the displaytype used, a high Δ∈ and particularly low viscosities for particularlyshort response times.

Present Invention

Surprisingly, it has now been found that it is possible to achieveliquid-crystalline media having a suitably high Δ∈, a suitable phaserange and Δn which do not exhibit the disadvantages of the materialsfrom the prior art, or at least only do so to a significantly lesserextent.

These improved liquid-crystalline media according to the presentinvention comprise

-   -   one or more compounds of the formula I

in which

-   R¹ denotes alkyl, alkoxy, fluorinated alkyl or fluorinated alkoxy    having 1 to 7 C atoms, alkenyl, alkenyloxy, alkoxyalkyl or    fluorinated alkenyl having 2 to 7 C. atoms and preferably alkyl or    alkenyl,-   Z¹¹ and Z¹², independently of one another, denote —CH₂CH₂—,    —CF₂CF₂—, —COO—, trans-CH═CH—, trans-CF═CF—, —CH₂O—, —CF₂O— or a    single bond, preferably —CH₂CH₂—, —COO—, trans-CH═CH— or a single    bond, particularly preferably —CF₂O— or a single bond and very    preferably a single bond,-   L¹¹ and L¹², independently of one another, denote H, F or Cl,    preferably H or F, preferably one or both and particularly    preferably both denote F, and-   X¹ denotes F, Cl, —CFH₂, —CF₂H, —CF₃, —OCF₂H or —OCF₃, preferably F,    and    -   optionally one or more compounds selected from the group of the        compounds of the formulae II and III:

in which

-   R² and R³, independently of one another, denote alkyl, alkoxy,    fluorinated alkyl or fluorinated alkoxy having 1 to 7 C atoms,    alkenyl, alkenyloxy, alkoxyalkyl or fluorinated alkenyl having 2 to    7 C atoms, and R² and R³ preferably denote alkyl or alkenyl,

-   -   on each appearance, independently of one another, denote

-   -   preferably

-   L²¹, L²², L³¹ and L³², independently of one another, denote H or F,    L²¹ and/or L³¹ preferably denote F,-   X² and X³, independently of one another, denote halogen, halogenated    alkyl or alkoxy having 1 to 3 C atoms or halogenated alkenyl or    alkenyloxy having 2 or 3 C atoms, preferably F, Cl, —OCF₃ or —CF₃,    very preferably F, Cl or —OCF₃,-   Z³ denotes —CH₂CH₂—, —CF₂CF₂—, —COO—, trans-CH═CH—, trans-CF═CF—,    —CH₂O— or a single bond, preferably —CH₂CH₂—, —COO—, trans-CH═CH— or    a single bond and very preferably —COO—, trans-CH═CH— or a single    bond, and-   m and n, independently of one another, denote 0, 1, 2 or 3,-   m preferably denotes 1, 2 or 3, and-   n preferably denotes 0, 1 or 2 and particularly preferably 1 or 2,    where, in the case of formula II, compounds of the formula I are    excluded, and    -   optionally one or more compounds of the formula IV

in which

-   R⁴¹ and R⁴², independently of one another, have the meaning    indicated for R² above under formula II, preferably R^(4l) denotes    alkyl and R⁴² denotes alkyl or alkoxy or R⁴¹ denotes alkenyl and R⁴²    denotes alkyl,

-   -   independently of one another and, if

-   -   occurs twice, also these independently of one another, denote

-   -   preferably one or more of

-   Z⁴¹ and Z⁴², independently of one another and, if Z⁴¹ occurs twice,    also these independently of one another, denote —CH₂CH₂—, —COO—,    trans-CH═CH—, trans-CF═CF—, —CH₂O—, —CF₂O—, —CE-C— or a single bond,    preferably one or more of them denote a single bond, and-   p denotes 0, 1 or 2, preferably 0 or 1.

The compounds of the formulae I, II and III are preferablydielectrically positive compounds, preferably having a dielectricanisotropy of greater than 3.

The compounds of the formula IV are preferably dielectrically neutralcompounds, preferably having a dielectric anisotropy in the range from−1.5 to 3.

The liquid-crystalline media according to the present applicationpreferably comprise in total 1 to 50%, preferably 1 to 30%, of compoundsof the formula I.

The individual compounds of the formula I and optionally the compoundsof the formulae II and/or III are employed in a concentration of 1 to20%, preferably 1 to 15%. These limits apply, in particular, if in eachcase two or more homologous compounds, i.e. compounds of the sameformula, are employed. If only a single substance, i.e. only onehomologue, of the compounds of a formula is employed, concentration canbe in the range from 2 to 20%, preferably from 3 to 14%.

In a preferred embodiment of the present invention, the media accordingto the invention in each case comprise one or more compounds of theformula I selected from the group of the compounds of the formulae I-1to I-3, preferably of the formula I-3:

in which R¹ has the meaning indicated above under formula I.

In addition to the compounds selected from the group of the compounds ofthe formula I, or preferred sub-formulae thereof, the media according tothe present invention preferably comprise one or more dielectricallypositive compounds having a dielectric anisotropy of greater than 3,selected from the group of the formulae II and III.

In a preferred embodiment of the present invention, the media accordingto the invention comprise one or more compounds selected from the groupof the compounds of the formulae II-1 to II-4, preferably of theformulae II-1 and/or II-2:

in which the parameters have the respective meanings indicated aboveunder formula II, and L²³ and L²⁴, independently of one another, denoteH or F, preferably L²³ denotes F, and

has one of the meanings given for

and, in the case of the formulae II-1 and II-4, X² preferably denotes For OCF₃, particularly preferably F, and, in the case of the formulaII-3,

independently of one another, preferably denote

where the compounds of the formula I are excluded,and/or selected from the group of the compounds of the formulae III-1and III-2:

in which the parameters have the meaning given under formula III.

In a preferred embodiment, the media according to the present inventionalternatively or in addition to the compounds of the formulae III-1and/or III-2 comprise one or more compounds of the formula III-3

in which the parameters have the respective meanings indicated above,and the parameters L³¹ and L³², independently of one another and of theother parameters, denote H or F.

The media according to the invention preferably comprise one or morecompounds selected from the group of the compounds of the formulae II-1to II-4 in which L²¹ and L²² and/or L²³ and L²⁴ both denote F.

In a preferred embodiment, the media comprise one or more compoundswhich are selected from the group of the compounds of the formulae II-2and II-4 in which L²¹, L²², L²³ and L²⁴ all denote F.

The media preferably comprise one or more compounds of the formula II-1.The compounds of the formula II-1 are preferably selected from the groupof the compounds of the formulae II-1a to II-1e:

in which the parameters have the respective meanings indicated above,and L²³ to L²⁶, independently of one another and of the otherparameters, denote H or F, and preferablyin formulae II-1a and II-1bL²¹ and L²² both denote F,in formulae II-1c and II-1d L²¹ and L²² both denote F and/or L²³ and L²⁴both denote F, andin formula II-1eL²¹, L²² and L²⁵ denote F, and in each case the other parameters havethe respective meanings given above.

Especially preferred compounds of the formula II-1 are

in which R² has the meaning indicated above.

The media preferably comprise one or more compounds of the formula II-2,which are preferably selected from the group of the compounds of theformulae II-2a to II-2j:

in which the parameters have the respective meanings indicated above,and L²⁵ to L²⁸, independently of one another, denote H or F, preferablyL²⁷ and L²⁸ both denote H, particularly preferably L²⁸ denotes H, andthe other parameters have the respective meanings given above, and wherethe compounds of the formula I are excluded.

The media according to the invention preferably comprise one or morecompounds selected from the group of the compounds of the formulae II-2ato II-2j in which L²¹ and L²² both denote F and/or L²³ and L²⁴ bothdenote F and the other parameters have the respective meanings givenabove.

In a preferred embodiment, the media according to the invention compriseone or more compounds selected from the group of the compounds of theformulae II-2a to II-2j in which L²¹, L²², L²³ and L²⁴ all denote F andthe other parameters have the respective meanings given above.

Especially preferred compounds of the formula II-2 are the compounds ofthe following formulae:

in which R² and X² have the meanings indicated above, and X² preferablydenotes F.

The media according to the invention preferably comprise one or morecompounds of the formula II-3, preferably selected from the group of thecompounds of the formulae II-3a to II-3c:

in which the parameters have the respective meanings indicated above,and L²¹ and L²² preferably both denote F.

In a preferred embodiment, the media according to the invention compriseone or more compounds of the formula II-4, preferably of the formulaII-4-a,

in which the parameters have the meaning given above, and X² preferablydenotes F or OCF₃, particularly preferably F.

The media according to the invention preferably comprise one or morecompounds of the formula III-1, preferably selected from the group ofthe compounds of the formulae III-1a and III-1b:

in which the parameters have the respective meanings indicated above,and the parameters L³³ and L³⁴, independently of one another and of theother parameters, denote H or F.

The media according to the invention preferably comprise one or morecompounds of the formula III-1a, preferably selected from the group ofthe compounds of the formulae III-1a-1 to III-1a-6:

in which R has the meaning indicated above.

The media according to the invention preferably comprise one or morecompounds of the formula III-1b, preferably selected from the group ofthe compounds of the formulae. III-1 b-1 to III-1 b-4, preferably of theformula III-1b-4:

in which R³ has the meaning indicated above.

The media according to the invention preferably comprise one or morecompounds of the formula III-2, preferably selected from the group ofthe compounds of the formulae III-2a to III-2j:

in which the parameters have the meaning given above and preferably inwhich the parameters have the respective meanings indicated above, andthe parameters L³³, L³⁴, L³⁵ and L³⁶, independently of one another andof the other parameters, denote H or F.

The media according to the invention preferably comprise one or morecompounds of the formula III-2a, preferably selected from the group ofthe compounds of the formulae III-2a-1 to III-2a-5:

in which R³ has the meaning indicated above.

The media according to the invention preferably comprise one or morecompounds of the formula III-2b, preferably selected from the group ofthe compounds of the formulae III-2b-1 and III-2b-2, preferably of theformula III-2b-2:

in which R³ has the meaning indicated above.

The media according to the invention preferably comprise one or morecompounds of the formula III-2c, preferably selected from the group ofthe compounds of the formulae III-2c-1 to III-2c-5:

in which R³ has the meaning indicated above.

The media according to the invention preferably comprise one or morecompounds selected from the group of the compounds of the formulaeIII-2d and III-2e, preferably selected from the group of the compoundsof the formulae III-2d-1 and III-2e-1:

in which R³ has the meaning indicated above.

The media according to the invention preferably comprise one or morecompounds of the formula III-2f, preferably selected from the group ofthe compounds of the formulae III-2f-1 to III-2f-5:

in which R³ has the meaning indicated above.

The media according to the invention preferably comprise one or morecompounds of the formula III-2g, preferably selected from the group ofthe compounds of the formulae III-2g-1 to III-2g-5:

in which R³ has the meaning indicated above.

The media according to the invention preferably comprise one or morecompounds of the formula III-2h, preferably selected from the group ofthe compounds of the formulae III-2h-1 to III-2h-3, preferably of theformula III-2h-3:

in which the parameters have the meaning given above, and X³ preferablydenotes F.

The media according to the invention preferably comprise one or morecompounds of the formula III-2i, preferably selected from the group ofthe compounds of the formulae III-2i-1 and III-2i-2, preferably of theformula III-2i-2:

in which the parameters have the meaning given above, and X³ preferablydenotes F.

The media according to the invention preferably comprise one or morecompounds of the formula III-2j, preferably selected from the group ofthe compounds of the formulae III-2j-1 and III-2j-2, preferably of theformula III-2j-1:

in which the parameters have the meaning given above.

Alternatively or in addition to the compounds of the formulae III-1and/or III-2, the media according to the present invention may compriseone or more compounds of the formula III-3

in which the parameters have the respective meanings indicated aboveunder formula III.

These compounds are preferably selected from the group of the formulaeIII-3a and III-3b:

in which R³ has the meaning indicated above.

The liquid-crystalline media according to the present inventionpreferably comprise a dielectrically neutral component, component C.This component has a dielectric anisotropy in the range from −1.5 to 3.It preferably comprises, more preferably predominantly consists of, evenmore preferably essentially consists of and especially preferablyentirely consists of dielectrically neutral compounds having adielectric anisotropy in the range from −1.5 to 3. This componentpreferably comprises, more preferably predominantly consists of, evenmore preferably essentially consists of and very preferably entirelyconsists of one or more dielectrically neutral compounds of the formulaIV having a dielectric anisotropy in the range from −1.5 to 3.

The dielectrically neutral component, component C, preferably comprisesone or more compounds selected from the group of the compounds of theformulae IV-1 to IV-6:

in which R⁴¹ and R⁴² have the respective meanings indicated above underformula IV, and in formulae IV-1, IV-5 and IV-6 R⁴¹ preferably denotesalkyl or alkenyl, preferably alkenyl, and R⁴² preferably denotes alkylor alkenyl, preferably alkyl, in formula IV-2 R⁴¹ and R⁴² preferablydenote alkyl, and in formula IV-4 R⁴¹ preferably denotes alkyl oralkenyl, more preferably alkyl, and R⁴² preferably denotes alkyl oralkoxy, more preferably alkoxy.

The dielectrically neutral component, component C, preferably comprisesone or more compounds selected from the group of the compounds of theformulae IV-1, IV-4, IV-5 and IV-6, preferably one or more compounds ofthe formula IV-1 and one or more compounds selected from the group ofthe formulae IV-4 and IV-5, more preferably one or more compounds ofeach of the formulae IV-1, IV-4 and IV-5 and very preferably one or morecompounds of each of the formulae IV-1, IV-4, IV-5 and IV-6.

In a preferred embodiment, the media according to the invention compriseone or more compounds of the formula IV-5, more preferably selected fromthe respective sub-formulae thereof of the formulae CCP-V-n and/orCCP-nV-m and/or CCP-Vn-m, more preferably of the formulae CCP-V-n and/orCCP-V2-n and very preferably selected from the group of the formulaeCCP-V-1 and CCP-V2-1. The definitions of these abbreviations (acronyms)are indicated below in Table D or are evident from Tables A to C.

In a likewise preferred embodiment, the media according to the inventioncomprise one or more compounds of the formula IV-1, more preferablyselected from the respective sub-formulae thereof of the formulaeCC-n-m, CC-n-V, CC-n-Vm, CC-V-V, CC-V-Vn and/or CC-nV-Vm, morepreferably of the formulae CC-n-V and/or CC-n-Vm and very preferablyselected from the group of the formulae CC-3-V, CC-4-V, CC-5-V, CC-3-V1,CC-4-V1, CC-5-V1, CC-3-V2 and CC-V-V1. The definitions of theseabbreviations (acronyms) are likewise indicated below in Table D or areevident from Tables A to C.

In a further preferred embodiment of the present invention, which may bethe same as the previous one or a different one, the liquid-crystalmixtures according to the present invention comprise component C whichcomprises, preferably predominantly consists of and very preferablyentirely consists of compounds of the formula IV selected from the groupof the compounds of the formulae IV-1 to IV-6 as shown above andoptionally of the formulae IV-7 to IV-13:

in which

-   R⁴¹ and R⁴², independently of one another, denote alkyl, alkoxy,    fluorinated alkyl or fluorinated alkoky having 1 to 7 C atoms,    alkenyl, alkenyloxy, alkoxyalkyl or fluorinated alkenyl having 2 to    7 C atoms, and-   L⁴ denotes H or F.

In a preferred embodiment, the media according to the invention compriseone or more compounds of the formula IV-8, more preferably selected fromthe respective sub-formulae thereof of the formulae CPP-3-2, CPP-5-2 andCGP-3-2, more preferably of the formulae CPP-3-2 and/or CGP-3-2 and veryparticularly preferably of the formula CPP-3-2. The definitions of theseabbreviations (acronyms) are indicated below in Table D or are evidentfrom Tables A to C.

The liquid-crystalline media according to the present inventionpreferably comprise one or more compounds of the formula V

in which

-   R⁵¹ and R⁵², independently of one another, have the meaning    indicated for R² above under formula II, preferably R⁵¹ denotes    alkyl and R⁵² denotes alkyl or alkenyl,

-    and, if it occurs twice, independently of one another on each    occurrence, denotes

-    preferably one or more of

-    denote

-   Z⁵¹ and Z⁵², independently of one another and, if Z⁵¹ occurs twice,    also these independently of one another, denote —CH₂CH₂—, —COO—,    trans-CF═CF—, —CH₂O—, —CF₂O— or a single bond, preferably one or    more of them denote(s) a single bond, and-   r denotes 0, 1 or 2, preferably 0 or 1, particularly preferably 1.

The compounds of the formula V are preferably dielectrically neutralcompounds having a dielectric anisotropy in the range from −1.5 to 3.

The media according to the invention preferably comprise one or morecompounds selected from the group of the compounds of the formulae V-1and V-2:

in which R⁵¹ and R⁵² have the respective meanings indicated above underformula V, and R⁵¹ preferably denotes alkyl, and in formula V-1 R⁵²preferably denotes alkenyl, preferably —(CH₂)₂—CH═CH—CH₃, and in formulaV-2 R⁵² preferably denotes alkyl or alkenyl, preferably —(CH₂)₂—CH═CH₂or —(CH₂)₂—CH═CH—CH₃.

The media according to the invention preferably comprise one or morecompounds selected from the group of the compounds of the formulae V-1and V-2 in which R⁵¹ preferably denotes n-alkyl, and in formula V-1 R⁵²preferably denotes alkenyl, and in formula V-2 R⁵² preferably denotesn-alkyl.

In a preferred embodiment, the media according to the invention compriseone or more compounds of the formula V-1, more preferably of thesub-formula PP-n-2Vm thereof, even more preferably of the formulaPP-1-2V1. The definitions of these abbreviations (acronyms) areindicated below in Table D or are evident from Tables A to C.

In a preferred embodiment, the media according to the invention compriseone or more compounds of the formula V-2, more preferably of thesub-formulae POP-n-m, PGP-n-2V and PGP-n-2Vm thereof, even morepreferably of the sub-formulae PGP-3-m, PGP-n-2V and PGP-n-V1 thereof,very preferably selected from the formulae PGP-3-2, PGP-3-3, PGP-3-4,PGP-3-5, PGP-1-2V, PGP-2-2V and PGP-3-2V. The definitions of theseabbreviations (acronyms) are likewise indicated below in Table D or areevident from Tables A to C.

Alternatively or in addition to the compounds of the formulae II and/orIII, the media according to the present invention may comprise one ormore dielectrically positive compounds of the formula VI

in which

-   R⁶ denotes alkyl, alkoxy, fluorinated alkyl or fluorinated alkoxy    having 1 to 7 C atoms; alkenyl, alkenyloxy, alkoxyalkyl or    fluorinated alkenyl having 2 to 7 C atoms and preferably alkyl or    alkenyl,

-    independently of one another, denote

-   L⁶¹ and L⁶², independently of one another, denote H or F, preferably    L⁶¹ denotes F, and-   X⁶ denotes halogen, halogenated alkyl or alkoxy having 1 to 3 C    atoms or halogenated alkenyl or alkenyloxy having 2 or 3 C atoms,    preferably F, Cl, —OCF₃ or —CF₃, very preferably F, Cl or —OCF₃,-   Z⁶ denotes —CH₂CH₂—, —CF₂CF₂—, —COO—, trans-CH═CH—, trans-CF═CF—,    —CH₂O— or —CF₂O—, preferably —CH₂CH₂—, —COO— or trans-CH═CH— and    very preferably —COO— or trans-CH═CH—, and-   q denotes 0 or 1.

The media according to the present invention preferably comprise one ormore compounds of the formula VI, preferably selected from the group ofthe compounds of the formulae VI-1 and VI-2:

in which the parameters have the respective meanings indicated above,and the parameters L⁶³ and L⁶⁴, independently of one another and of theother parameters, denote H or F, and Z⁶ preferably denotes —CH₂—CH₂—.

The compounds of the formula VI-1 are preferably selected from the groupof the compounds of the formulae VI-1a and VI-1b:

in which R⁶ has the meaning indicated above.

The compounds of the formula VI-2 are preferably selected from the groupof the compounds of the formulae VI-2a to VI-2d:

in which R⁶ has the meaning indicated above.

In addition, the liquid-crystal media according to the present inventionmay comprise one or more compounds of the formula VII

in which

-   R⁷ has the meaning indicated for R² above under formula II,-   one of

-    which is present denotes

-    preferably

-    preferably

-   10 denotes

-   and the others have the same meaning or, independently of one    another, denote

-    preferably

-   Z⁷¹ and Z⁷², independently of one another, denote —CH₂CH₂—, —COO—,    trans-CH═CH—, trans-CF═CF—, —CH₂O—, —CF₂O— or a single bond,    preferably one or more of them denote(s) a single bond and very    preferably both denote a single bond,-   t denotes 0, 1 or 2, preferably 0 or 1, more preferably 1, and-   X⁷ has the meaning indicated for X² above under formula II or    alternatively, independently of R⁷, may have one of the meanings    indicated for R⁷.

The compounds of the formula VII are preferably dielectrically positivecompounds.

In addition, the liquid-crystal media according to the present inventionmay comprise one or more compounds of the formula VIII

in which

-   R⁸¹ and R⁸², independently of one another, have the meaning    indicated for R² above under formula II, and

-    denotes

-    preferably

-    denotes

-   Z⁸¹ and Z⁸² independently of one another, denote —CH₂CH₂—, —COO—,    trans-CH═CH—, trans-CF═CF—, —CH₂O—, —CF₂O— or a single bond,    preferably one or more of them denote(s) a single bond and very    preferably both denote a single bond,-   L⁸¹ and L⁸², independently of one another, denote C—F or N,    preferably one of L⁸¹ and L⁸² or both denote(s) C—F and very    preferably both denote C—F, and-   s denotes 0 or 1.

The compounds of the formula VIII are preferably dielectrically negativecompounds.

The media according to the invention preferably comprise one or morecompounds of the formula VIII, preferably selected from the group of thecompounds of the formulae VIII-1 to VIII-3:

in which

-   R⁸¹ and R⁸² have the respective meanings indicated above under    formula VIII.

In formulae VIII-1 to VIII-3, R⁸¹ preferably denotes n-alkyl or1-E-alkenyl and R⁸² preferably denotes n-alkyl or alkoxy.

The liquid-crystalline media according to the present inventionpreferably comprise one or more compounds selected from the group of thecompounds of the formulae I to VIII, preferably of the formulae I to VIIand more preferably of the formulae I and II and/or III and/or IV and/orVI. They particularly preferably predominantly consist of, even morepreferably essentially consist of and very preferably entirely consistof these compounds.

In this application, “comprise” in connection with compositions meansthat the relevant entity, i.e. the medium or the component, comprisesthe component or components or compound or compounds indicated,preferably in a total concentration of 10% or more and very preferably20% or more.

In this connection, “predominantly consist of” means that the relevantentity comprises 55% or more, preferably 60% or more and very preferably70% or more of the component or components or the compound or compoundsindicated.

In this connection, “essentially consist of” means that the relevantentity comprises 80% or more, preferably 90% or more and very preferably95% or more of the component or components or the compound or compoundsindicated.

In this connection, “virtually completely consist of” or “entirelyconsist of” means that the relevant entity comprises 98% or more,preferably 99% or more and very preferably 100.0% of the component orcomponents or the compound or compounds indicated.

Other mesogenic compounds which are not explicitly mentioned above canoptionally and advantageously also be used in the media according to thepresent invention. Such compounds are known to the person skilled in theart.

The liquid-crystal media according to the present invention preferablyhave a clearing point of 60° C. or more, more preferably 65° C. or more,particularly preferably 70° C. or more and very particularly preferably75° C. or more.

The nematic phase of the media according to the invention preferablyextends at least from 0° C. or less to 70° C. or more, more preferablyat least from −20° C. or less to 75° C. or more, very preferably atleast from −30° C. or less to 75° C. or more and in particular at leastfrom −40° C. or less to 80° C. or more.

The Δ∈ of the liquid-crystal medium according to the invention, at 1 kHzand 20° C., is preferably 2 or more, more preferably 4 or more and verypreferably 6 or more. In particular, Δ∈ is 20 or less.

The Δn of the liquid-crystal media according to the present invention,at 589 nm (Na^(D)) and 20° C., is preferably in the range from 0.070 ormore to 0.150 or less, more preferably in the range from 0.080 or moreto 0.140 or less, even more preferably in the range from 0.090 or moreto 0.135 or less and very particularly preferably in the range from0.100 or more to 0.130 or less.

Ina preferred embodiment of the present application, the Δn of theliquid-crystal media according to the present invention is preferably0.080 or more, more preferably 0.090 or more.

In this preferred embodiment of the present invention, the Δn of theliquid-crystal media is preferably in the range from 0.090 or more to0.120 or less, more preferably in the range from 0.095 or more to 0.115or less and very particularly preferably in the range from 0.100 or moreto 0.105 or less, while Δ∈ is preferably in the range from 5 or more to11 or less, preferably in the range from 6 or more to 10 or less andparticularly preferably in the range from 7 or more to 9 or less.

In this embodiment, the nematic phase of the media according to theinvention preferably extends at least from −20° C. or less to 70° C. ormore, more preferably at least from −20° C. or less to 70° C. or more,very preferably at least from −30° C. or less to 70° C. or more and inparticular at least from −40° C. or less to 95° C. or more.

In accordance with the present invention, the compounds of the formula Itogether are preferably used in the media in a total concentration of 1%to 50%, more preferably 1% to 30%, even more preferably 2% to 30%, evenmore preferably 3% to 30% and very preferably 5% to 25% of the mixtureas a whole.

The compounds selected from the group of the formulae II and III arepreferably used in a total concentration of 2% to 60%, more preferably3% to 35%, even more preferably 4% to 20% and very preferably 5% to 15%of the mixture as a whole.

The compounds of the formula IV are preferably used in a totalconcentration of 5% to 70%, more preferably 20% to 65%, even morepreferably 30% to 60% and very preferably 40% to 55% of the mixture as awhole.

The compounds of the formula V are preferably used in a totalconcentration of 0% to 30%, more preferably 0% to 15% and verypreferably 1% to 10% of the mixture as a whole.

The compounds of the formula VI are preferably used in a totalconcentration of 0% to 50%, more preferably 1% to 40%, even morepreferably 5% to 30% and very preferably 10% to 20% of the mixture as awhole.

The media according to the invention may optionally comprise furtherliquid-crystal compounds in order to adjust the physical properties.Such compounds are known to the person skilled in the art. Theirconcentration in the media according to the present invention ispreferably 0% to 30%, more preferably 0.1% to 20% and very preferably 1%to 15%.

In a preferred embodiment, the concentration of the compound of theformula CC-3-V in the media according to the invention can be 50% to65%, particularly preferably 55% to 60%.

The liquid-crystal media preferably comprise in total 50% to 100%, morepreferably 70% to 100% and very preferably 80% to 100% and in particular90% to 100% of the compounds of the formulae I to VII, preferablyselected from the group of the compounds of the formulae I to VI,particularly preferably of the formulae I to V, in particular of theformulae I, II, III, IV, V and VII and very particularly preferably ofthe formulae I, II, III, IV and V. They preferably predominantly consistof and very preferably virtually completely consist of these compounds.In a preferred embodiment, the liquid-crystal media in each casecomprise one or more compounds of each of these formulae.

In the present application, the expression dielectrically positivedescribes compounds or components where Δ∈>3.0, dielectrically neutraldescribes those where −1.5≦Δ∈≦3.0 and dielectrically negative describesthose where Δ∈<−1.5. Δ∈ is determined at a frequency of 1 kHz and at 20°C. The dielectric anisotropy of the respective compound is determinedfrom the results of a solution of 10% of the respective individualcompound in a nematic host mixture. If the solubility of the respectivecompound in the host mixture is less than 10%, the concentration isreduced to 5%. The capacitances of the test mixtures are determined bothin a cell having homeotropic alignment and in a cell having homogeneousalignment. The cell thickness of both types of cells is approximately 20μm. The voltage applied is a rectangular wave having a frequency of 1kHz and an effective value of typically 0.5 V to 1.0 V, but it is alwaysselected to be below the capacitive threshold of the respective testmixture.

Δ∈ is defined as (∈_(∥)−∈_(⊥)), while ∈_(av). is (∈_(∥)+2∈_(⊥))/3.

The host mixture used for dielectrically positive compounds is mixtureZLI-4792 and that used for dielectrically neutral and dielectricallynegative compounds is mixture ZLI-3086, both from Merck KGaA, Germany.The absolute values of the dielectric constants of the compounds aredetermined from the change in the respective values of the host mixtureon addition of the compounds of interest. The values are extrapolated toa concentration of the compounds of interest of 100%.

Components having a nematic phase at the measurement temperature of 20°C. are measured as such, all others are treated like compounds.

The expression threshold voltage in the present application refers tothe optical threshold and is quoted for 10% relative contrast (V₁₀), andthe expression saturation voltage refers to the optical saturation andis quoted for 90% relative contrast (V₉₀), in both cases unlessexpressly stated otherwise. The capacitive threshold voltage (V₀), alsocalled the Freedericks threshold (V_(Fr)), is only used if expresslymentioned.

The ranges of the parameters indicated in this application all includethe limit values, unless expressly stated otherwise.

The different upper and lower limit values indicated for various rangesof properties in combination with one another give rise to additionalpreferred ranges.

Throughout this application, the following conditions and definitionsapply, unless expressly stated otherwise. All concentrations areindicated in percent by weight and relate to the respective mixture as awhole, all temperatures are quoted in degrees Celsius and alltemperature differences are quoted in differential degrees. All physicalproperties are determined in accordance with “Merck Liquid Crystals,Physical Properties of Liquid Crystals”, Status November 1997, MerckKGaA, Germany and are quoted for a temperature of 20° C., unlessexpressly stated otherwise. The optical anisotropy (Δn) is determined ata wavelength of 589.3 nm. The dielectric anisotropy (Δ∈) is determinedat a frequency of 1 kHz. The threshold voltages, as well as all otherelectro-optical properties, are determined using test cells produced atMerck KGaA, Germany. The test cells for the determination of Δ∈ have acell thickness of approximately 20 μm. The electrode is a circular ITOelectrode having an area of 1.13 cm² and a guard ring. The orientationlayers are SE-1211 from Nissan Chemicals, Japan, for homeotropicorientation (∈_(∥)) and polyimide AL-1054 from Japan Synthetic Rubber,Japan, for homogeneous orientation (∈_(⊥)). The capacitances aredetermined using a Solatron 1260 frequency response analyser using asine wave with a voltage of 0.3 V_(rms). The light used in theelectro-optical measurements is white light. A set-up using acommercially available DMS instrument from Autronic-Melchers, Germany,is used here. The characteristic voltages have been determined underperpendicular observation. The threshold (V₁₀), mid-grey (V₅₀) andsaturation (V₉₀) voltages have been determined for 10%, 50% and 90%relative contrast, respectively.

The liquid-crystal media according to the present invention may comprisefurther additives and chiral dopants in the usual concentrations. Thetotal concentration of these further constituents is in the range from0% to 10%, preferably 0.1% to 6%, based on the mixture as a whole. Theconcentrations of the individual compounds used are each preferably inthe range from 0.1% to 3%. The concentration of these and similaradditives is not taken into consideration when quoting the values andconcentration ranges of the liquid-crystal components and compounds ofthe liquid-crystal media in this application.

The liquid-crystal media according to the invention consist of aplurality of compounds, preferably 3 to 30, more preferably 4 to 20 andvery preferably 4 to 16 compounds. These compounds are mixed in aconventional manner. In general, the desired amount of the compound usedin the smaller amount is dissolved in the compound used in the largeramount. If the temperature is above the clearing point of the compoundused in the higher concentration, it is particularly easy to observecompletion of the dissolution process. It is, however, also possible toprepare the media in other conventional ways, for example usingso-called pre-mixes, which can be, for example, homologous or eutecticmixtures of compounds, or using so-called “multibottle” systems, theconstituents of which are themselves ready-to-use mixtures.

By addition of suitable additives, the liquid-crystal media according tothe present invention can be modified in such a way that they can beused in all known types of liquid-crystal displays, either using theliquid-crystal media as such, such as TN, TN-AMD, ECB-AMD, VAN-AMD,IPS-AMD, FFS-AMD LCDs, or in composite systems, such as PDLC, NCAP, PNLCDs and especially in ASM-PA LCDs.

All temperatures, such as, for example, the melting point T(C,N) orT(C,S), the transition from the smectic (S) to the nematic (N) phaseT(S,N) and the clearing point T(N,I) of the liquid crystals, are quotedin degrees Celsius. All temperature differences are quoted indifferential degrees.

In the present invention and especially in the following examples, thestructures of the mesogenic compounds are indicated by means ofabbreviations, also called acronyms. In these acronyms, the chemicalformulae are abbreviated as follows using Tables A to C below. Allgroups C_(n)H_(2n+1), C_(m)H_(2m+1) and C_(l)H_(2l+1) or C_(n)H_(2n-1),C_(m)H_(2m−1) and C_(l)H_(2l−1) denote straight-chain alkyl or alkenyl,preferably 1E-alkenyl, each having n, m and l C atoms respectively.Table A lists the codes used for the ring elements of the corestructures of the compounds, while Table B shows the linking groups.Table C gives the meanings of the codes for the left-hand or right-handend groups. The acronyms are composed of, the codes for the ringelements with optional linking groups, followed by a first hyphen andthe codes for the left-hand end group, and a second hyphen and the codesfor the right-hand end group. Table D shows illustrative structures ofcompounds together with their respective abbreviations.

TABLE A Ring elements C

P

D

DI

A

AI

G

GI

U

UI

Y

M

MI

N

NI

Np

dH

N3f

N3fI

tH

tHI

tH2f

tH2fI

K

KI

L

LI

F

FI

TABLE B Linking groups E —CH₂CH₂— Z —CO—O— V —CH═CH— ZI —O—CO— X —CF═CH—O —CH₂—O— XI —CH═CF— OI —O—CH₂— B —CF═CF— Q —CF₂—O— T —C≡C— QI —O—CF₂— W—CF₂CF₂— T —C≡C—

TABLE C End groups Left-hand side Right-hand side Use alone -n-C_(n)H_(2n+1)— -n —C_(n)H_(2n+1) -nO- C_(n)H_(2n+1)—O— -nO—O—C_(n)H_(2n+1) -V- CH₂═CH— -V —CH═CH₂ -nV- C_(n)H_(2n+1)—CH═CH— -nV—C_(n)H_(2n)—CH═CH₂ -Vn- CH₂═CH—C_(n)H_(2n+1)— -Vn —CH═CH—C_(n)H_(2n+1)-nVm- C_(n)H_(2n+1)—CH═CH—C_(m)H_(2m)— -nVm—C_(n)H_(2n)—CH═CH—C_(m)H_(2m+1) -N- N≡C— -N —C≡N -S- S═C═N— -S —N═C═S-F- F— -F —F -CL- Cl— -CL —Cl -M- CFH₂— -M —CFH₂ -D- CF₂H— -D —CF₂H -T-CF₃— -T —CF₃ -MO- CFH₂O— -OM —OCFH₂ -DO- CF₂HO— -OD —OCF₂H -TO- CF₃O—-OT —OCF₃ -OXF- CF₂═CH—O— -OXF —O—CH═CF₂ -A- H—C≡C— -A —C≡C—H -nA-C_(n)H_(2n+1)—C≡C— -An —C≡C—C_(n)H_(2n+1) -NA- N≡C—C≡C— -AN —C≡C—C≡N Usetogether with one another and with others - . . . A . . . - —C≡C— - . .. A . . . —C≡C— - . . . V . . . - CH═CH— - . . . V . . . —CH═CH— - . . .Z . . . - —CO—O— - . . . Z . . . —CO—O— - . . . ZI . . . - —O—CO— - . .. ZI . . . —O—CO— - . . . K . . . - —CO— - . . . K . . . —CO— - . . . W. . . - —CF═CF— - . . . W . . . —CF═CF—in which n and m each denote integers, and the three dots “ . . . ” arespacers for other abbreviations from this table.

The following table shows illustrative structures together with theirrespective abbreviations. These are shown in order to illustrate themeaning of the rules for the abbreviations. They furthermore representcompounds which are preferably used.

TABLE D Illustrative structures

The following table, Table E, shows illustrative compounds which can beused as stabiliser in the mesogenic media according to the presentinvention.

TABLE E

In a preferred embodiment of the present invention, the mesogenic mediacomprise one or more compounds selected from the group of the compoundsfrom Table E.

The following table, Table F, shows illustrative compounds which canpreferably be used as chiral dopants in the mesogenic media according tothe present invention.

TABLE F

In a preferred embodiment of the present invention, the mesogenic mediacomprise one or more compounds selected from the group of the compoundsfrom Table F.

The mesogenic media according to the present application preferablycomprise two or more, preferably four or more, compounds selected fromthe group consisting of the compounds from the above tables.

The liquid-crystal media according to the present invention preferablycomprise

-   -   seven or more, preferably eight or more, compounds, preferably        compounds having three or more, preferably four or more,        different formulae, selected from the group of the compounds        from Table D.

EXAMPLES

The examples below illustrate the present invention without limiting itin any way.

However, the physical properties show the person skilled in the art whatproperties can be achieved and in what ranges they can be modified. Inparticular, the combination of the various properties which canpreferably be achieved is thus well defined for the person skilled inthe art.

Liquid-crystal mixtures having the composition and properties asindicated in the following tables are prepared.

Example 1

Composition Compound No. Abbreviation c/% 1 PGPQP-3-F 6.0 2 APUQU-2-F9.0 3 APUQU-3-F 8.0 4 CDU-2-F 5.0 5 PGU-2-F 9.0 6 PGU-3-F 3.0 7 CC-3-V45.0 8 CC-3-V1 6.0 9 CCP-V-1 9.0 Σ 100.0 Physical properties T(N, I) =74.0° C. n_(e) (20° C., 589.3 nm) = 1.5860 Δn (20° C., 589.3 nm) =0.1010 ε_(||) (20° C., 1 kHz) = 11.9 Δε (20° C., 1 kHz) = 8.4 γ₁ (20°C.) = 58 mPa · s V₀ (20° C.) = 1.24 V

Example 2

Composition Compound No. Abbreviation c/% 1 PGPQU-3-F 6.0 2 APUQU-2-F8.0 3 APUQU-3-F 7.0 4 CDU-2-F 4.5 5 PGU-2-F 9.0 6 PGU-3-F 3.0 7 CC-3-V44.0 8 CC-3-V1 6.5 9 CCP-V-1 12.0 Σ 100.0 Physical properties T(N, I) =74.0° C. n_(e) (20° C., 589.3 nm) = 1.5852 Δn (20° C., 589.3 nm) =0.0999 ε_(||) (20° C., 1 kHz) = 11.9 Δε (20° C., 1 kHz) = 8.5 γ₁ (20°C.) = 57 mPa · s V₀ (20° C.) = 1.24 V

Example 3

Composition Compound No. Abbreviation c/% 1 PGPQU-3-F 6.0 2 APUQU-2-F7.0 3 APUQU-3-F 6.0 4 PGUQU-3-F 7.5 5 PGU-2-F 7.0 6 CC-3-V 55.0 7CCP-V-1 11.5 Σ 100.0 Physical properties T(N, I) = 74.5° C. n_(e) (20°C., 589.3 nm) = 1.5844 Δn (20° C., 589.3 nm) = 0.0999 ε_(||) (20° C., 1kHz) = 11.2 Δε (20° C., 1 kHz) = 8.0 γ₁ (20° C.) = 53 mPa · s V₀ (20°C.) = 1.27 V

Example 4

Composition Compound No. Abbreviation c/% 1 PGPQU-3-F 6.0 2 APUQU-2-F9.0 3 APUQU-3-F 9.0 4 PGUQU-3-F 8.0 5 CC-3-V 59.0 6 CCP-V-1 3.0 7PGP-2-3 2.0 8 PGP-2-4 4.0 Σ 100.0 Physical properties T(N, I) = 73.0° C.n_(e) (20° C., 589.3 nm) = 1.5850 Δn (20° C., 589.3 nm) = 0.1017 ε_(||)(20° C., 1 kHz) = 11.4 Δε (20° C., 1 kHz) = 8.2 γ₁ (20° C.) = 53 mPa · s

These mixtures of Examples 1 to 4 are very highly suitable for displaysin IPS mode.

Example 5

Composition Compound No. Abbreviation c/% 1 PGPQP-3-F 4.0 2 PGUQU-3-F9.0 3 PGU-3-F 10.0 4 CC-3-V 39.0 5 CC-3-V1 8.0 6 CCP-V-1 4.0 7 PP-1-2V17.0 8 PGP-2-3 6.0 9 PGP-2-4 6.0 10 PGP-2-5 7.0 Σ 100.0 Physicalproperties T(N, I) = 75.0° C. n_(e) (20° C., 589.3 nm) = 1.6325 Δn (20°C., 589.3 nm) = 0.1368 ε_(||) (20° C., 1 kHz) = 7.6 Δε (20° C., 1 kHz) =4.7 γ₁ (20° C.) = 58 mPa · s V₁₀ (20° C.) = 2.04 V V₉₀ (20° C.) = 2.96 V

Example 6

Composition Compound No. Abbreviation c/% 1 PGPQU-3-F 5.0 2 PGUQU-3-F7.0 3 PGU-3-F 10.0 4 CC-3-V 38.0 5 CC-3-V1 8.0 6 CCP-V-1 6.0 7 PP-1-2V18.0 8 PGP-2-3 6.0 9 PGP-2-4 6.0 10 PGP-2-5 6.0 Σ 100.0 Physicalproperties T(N, I) = 74.0° C. n_(e) (20° C., 589.3 nm) = 1.6308 Δn (20°C., 589.3 nm) = 0.1352 ε_(||) (20° C., 1 kHz) = 7.7 Δε (20° C., 1 kHz) =4.7 γ₁ (20° C.) = 57 mPa · s V₁₀ (20° C.) = 2.02 V V₉₀ (20° C.) = 2.95 V

Example 7

Composition Compound No. Abbreviation c/% 1 PGPQU-3-F 6.0 2 PGUQU-3-F6.5 3 PGU-3-F 10.0 4 CC-3-V 38.5 5 CC-3-V1 8.0 6 CCP-V-1 5.0 7 PP-1-2V17.5 8 PGP-2-3 6.0 9 PGP-2-4 6.0 10 PGP-2-5 6.5 Σ 100.0 Physicalproperties T(N, I) = 74.0° C. n_(e) (20° C., 589.3 nm) = 1.6311 Δn (20°C., 589.3 nm) = 0.1357 ε_(||) (20° C., 1 kHz) = 7.8 Δε (20° C., 1 kHz) =4.8 γ₁ (20° C.) = 58 mPa · s V₁₀ (20° C.) = 2.00 V V₉₀ (20° C.) = 2.95 V

Example 8

Composition Compound No. Abbreviation c/% 1 PGPQU-3-F 5.0 2 PGUQU-3-F8.0 3 PGU-2-F 4.0 4 PGU-3-F 11.0 5 PUQU-3-F 10.0 6 CC-3-V 32.0 7 CC-3-V18.0 8 CCP-V-1 15.0 9 PGP-2-3 4.0 10 PGP-2-4 3.0 Σ 100.0 Physicalproperties T(N, I) = 74.5° C. n_(e) (20° C., 589.3 nm) = 1.6188 Δn (20°C., 589.3 nm) = 0.1264 ε_(||) (20° C., 1 kHz) = 12.6 Δε (20° C., 1 kHz)= 9.2 γ₁ (20° C.) = 65 mPa · s V₁₀ (20° C.) = 1.40 V V₉₀ (20° C.) = 2.12V

The mixtures of Examples 5 to 8 are very highly suitable for displays inTN mode. The mixtures of Examples 5 to 7 are particularly suitable fordisplays having 5 to 6 volt drivers, and the mixture of Example 8 isparticularly suitable for displays having 2.5 to 3 volt drivers.

1. A liquid-crystalline medium, comprising: one or more compounds offormula I

wherein R¹ denotes alkyl, alkoxy, fluorinated alkyl or fluorinatedalkoxy having 1 to 7 C atoms, alkenyl, alkenyloxy, alkoxyalkyl orfluorinated alkenyl having 2 to 7 C atoms, Z¹¹ and Z¹², independently ofone another, denote —CH₂CH₂—, —CF₂CF₂—, —COO—, trans-CH═CH—,trans-CF═CF—, —CH₂O—, —CF₂O— or a single bond, L¹¹ and L¹²,independently of one another, denote H, F or Cl, and X¹ denotes F, Cl,—CFH₂, —CF₂H, —CF₃, —OCF₂H or —OCF₃.
 2. The liquid-crystalline mediumaccording to claim 1, further comprising one or more compounds selectedfrom formulae II and III:

wherein R² and R³, independently of one another, denote alkyl, alkoxy,fluorinated alkyl or fluorinated alkoxy having 1 to 7 C atoms, alkenyl,alkenyloxy, alkoxyalkyl or fluorinated alkenyl having 2 to 7 C atoms,

 on each appearance, independently of one another, denote

L²¹, L²², L³¹ and L³², independently of one another, denote H or F, X²and X³, independently of one another, denote halogen, halogenated alkylor alkoxy having 1 to 3 C atoms or halogenated alkenyl or alkenyloxyhaving 2 or 3 C atoms, Z³ denotes —CH₂CH₂—, —CF₂CF₂—, —COO—,trans-CH═CH—, trans-CF═CF—, —CH₂O— or a single bond, and m and n,independently of one another, denote 0, 1, 2 or 3, wherein the compoundsof formula I are excluded from the compounds of formula II.
 3. Theliquid-crystalline medium according to claim 1, further comprising oneor more compounds of formula IV

in which R⁴¹ and R⁴², independently of one another, denote alkyl,alkoxy, fluorinated alkyl or fluorinated alkoxy having 1 to 7 C atoms,alkenyl, alkenyloxy, alkoxyalkyl or fluorinated alkenyl having 2 to 7 Catoms,

 independently of one another and, if

 occurs twice, also these independently of one another,  denote

Z⁴¹ and Z⁴², independently of one another and, if Z⁴¹ occurs twice, alsothese independently of one another, denote —CH₂CH₂—, —COO—,trans-CH═CH—, trans-CF═CF—, —CH₂O—, —CF₂O—, —C≡C— or a single bond, andp denotes 0, 1 or
 2. 4. The liquid-crystalline medium according to claim1, wherein the total concentration of the compounds of the formula I inthe medium is in the range from 1% to 50%.
 5. The liquid-crystallinemedium according to claim 2, wherein said medium comprises one or morecompounds of the formula II.
 6. The liquid-crystalline medium accordingto claim 2, wherein said medium comprises one or more compounds of theformula III.
 7. The liquid-crystalline medium according to claim 1,further comprising one or more dielectrically neutral compounds offormula V

wherein R⁵¹ and R⁵², independently of one another, denote alkyl, alkoxy,fluorinated alkyl or fluorinated alkoxy having 1 to 7 C atoms, alkenyl,alkenyloxy, alkoxyalkyl or fluorinated alkenyl having 2 to 7 C atoms,

 on each appearance, independently of one another, denote

 on each occurrence, independently of one another, denotes

Z⁵¹ and Z⁵², independently of one another and, if Z⁶¹ occurs twice, alsothese independently of one another, denote —CH₂CH₂—, —COO—,trans-CH═CH—, trans-CF═CF—, —CH₂O—, —CF₂O— or a single bond, and rdenotes 0, 1 or
 2. 8. A liquid-crystal display containing a mediumaccording to claim
 1. 9. The liquid-crystal display according to claim8, wherein said display is addressed by an active matrix.
 10. A methodof generating an electro-optical effect comprising subjecting theliquid-crystal display according to claim 8 to an electric field.
 11. Aprocess for the preparation of a medium according to claim 2, saidprocess comprising: mixing one or more compounds of the formula I withone or more of the compounds of formula II and/or formula III, and/orone or more further liquid-crystalline compounds, and/or one or moreadditives.
 12. The liquid-crystalline medium according to claim 1,wherein X¹ is F.
 13. The liquid-crystalline medium according to claim12, wherein L¹¹ and L¹² are both H.
 14. The liquid-crystalline mediumaccording to claim 12, wherein L¹¹ and L¹² are both F.
 15. Theliquid-crystalline medium according to claim 2, wherein the compounds ofthe formulae I, II and III have a dielectric anisotropy of greater than3.
 16. The liquid-crystalline medium according to claim 7, wherein thecompounds of the formula V have a dielectric anisotropy in the rangefrom −1.5 to
 3. 17. The liquid-crystalline medium according to claim 1,wherein said liquid-crystalline medium contains in total 1 to 50% ofcompounds of the formula I.
 18. The liquid-crystalline medium accordingto claim 1, wherein the compounds of formula I are selected fromformulae I-1 to I-3:

in which R¹ has the meaning indicated in claim
 1. 19. Theliquid-crystalline medium according to claim 2, wherein the compounds offormula II are selected from formulae II-1 to II-4:

wherein L²³ and L²⁴, independently of one another, denote H or F, and

and/or the compounds of formula III are selected from formulae III-1 andIII-2: